Diffusion furnace process tube

ABSTRACT

An improved process tube having a plurality of chambers on the process tunnel of the tube, two process gas chambers straddling the hot-zone of the process tube provide introduction and exhaust of process gases to the hot-zone, and two chambers straddling the process gas chambers provide gas curtains to restrict the process gases to the process tunnel intermediate the two process gas chambers.

* nited States Patent 1191 1111 3,11,26 Enderlein May 21, 1974 [5 DIFFUSION FURNACE PROCESS TUBE 2,253,897 8/ 1941 Doderer 432/23 1,643,775 9/1927 Kelleher 432/23 [75] lnvemor- Hans i Fr'edl'lch Konrad 2,994,522 8/1961 Albers-Schoenberg.... 432/18 Endeflem, Konstanl, Germany 3,723,053 3/1973 Myers et a1. 432/11 [73] Assignee: John B. Sowell, Ardmore, Pa.

Primary Examiner-John J. Camby' [22] Filed: 1972 Attorney, Agent, or FirmJohn B. Sowell [21] App]. No.: 303,652

I [57] ABSTRACT 52 us. c1 432/200, 432/11, 432/23 An improved Process tube having a plurality of cham- [51] 11m. (:1. F27b 5/04, F27b 11/08 hers on the Process tunnel of the tube two Process gas 5 Field f Search; 432 200 201 202 1 1 chambers straddling the hot-zone of the process tube 432 1 23 provide introduction and exhaust of process gases to the hot-zone, and two chambers straddling the process 5 References Cited gas chambers provide gas curtains to' restrict the pro- UNITED STATES PATENTS cess gases to the process tunnel intermediate the two I process gas chambers. 3,227,782 H1966 Gle et al. 432/11 3,581,679 1/1971 Jansen 432/202 8 Claims, 5 Drawing Figures PATENTEUIAYZ! m4 SHEEI 1 [If 2 DIFFUSION FURNACE PROCESS TUBE BACKGROUND or THE INVENTION Heretofore, process tubes for diffusion furnaces with cylindrical tubes had open ends and no intermediate connection points for the introduction of gases. Process gases were usually introduced at one end of the process tube and the semiconductor wafers to be treated or processed were both loaded and unloaded at the other end of the process tube. It has become desirable to continuously feed semiconductor wafers through a process tube in order to mechanize' loading and unloading of semiconductor wafers.

When some process gases are introduced into a process tube there is a tendency for the process gas to deposit on the colder portions of the process tube as well as on the semiconductor wafers. Tubes which collect deposits may easily contaminate a different process or even affect the rate of the same process.

BRIEF SUMMARY OF THE INVENTION The present invention substantially eliminates the cause for process gas deposits in the process tube and provides a more uniform processgas mixture in the hot-zone of the process tube where active processes occur. The means employed to achievethe invention do not block or interfere with the ends of the process tube, leaving it open and freely accessible for automatic mechanization equipment.to-continuously pass semiconductor wafers through the process tube.

In accomplishing the invention there is provided a process tube having a plurality of chambers affixed to the process tunnel of the tube intermediate the open ends of the process tunnel.

Oneprocess chamber is a plenum for mixing and introducing process gases into the process tunnel in front of the hot-zone. A second process chamber following the hot-zone exhausts the process gases from the process tunnel. Gas curtain chambers are provided intermediate the ends of the process tube and the process chambersto restrict the process gases to the process tunnel and to allow the ends of the tunnel to remain open and accessible for the continuous flow of semiconductor wafers through the process tunnel.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevation view of the present invention process tube.

FIG. 2 is a top view of the process tube shown in FIG. 1.

FIG. 3 is an elevation view in section taken at lines 33 of FIG. I showing the gas inlet end.

FIG. 4 is an elevation view in section taken at lines 44 of FIG. 1 showing the gas exhaust end.

FIG. 5 is an elevation view in section showing the exhaust chamber and exhaust line.

DESCRIPTION OF THE PREFERRED EMBODIMENT The process tube of the present invention is adapted to be used in a standard diffusion furnace such as those shown and described in US. Pat. No. 3,387,078.

Process tube is preferably made of quartz in order to contain highly corrosive or toxic gases and to resist temperatures in the range of 1,300 C. As is well known in the semiconductor art, a wafer 11 of silicon or other semiconductor material is placed on a holder or boat 12 and moved into the hot-zone where a process is conducted at high temperature; The holder 12 and wafer '11 are then removed from the hot-zone and another holder 12 with wafers 11 are placed in the hot-zone to be processed. For purposes of this description the hotzone comprises approximately half the length of process tube in the center of the tube where process gases are passed. It will be understood that the heating elements in the diffusion furnace, not shown, define the length of the hot-zone and the adjacent end zones are employed to control the holder 12 and wafer 11 at an accurate predetermined temperature. Process tubes 10 are usually placed inside ceramic protective tubes 9 which are adjacent to the heating elements in the furnace.

Basically three types of processes are conducted in the hot-zone. First, oxidization of the silicon wafer is performed by introducing water and/or oxygen. Secondly, deposition of dopants such as boron, phosphorous, antimony and arsenic, etc. are shallow-diffused by introduction of dopants and/or gases. Lastly, deep diffusion of the above dopants is performed by raising the hot-zone temperatures above those employed for deposition in the presence of controlled gases such as nitrogen, argon and/or oxygen.

Referring now to the figures, process tunnel 13 is shown to be preferably rectangular but could have other shapes. Four chambers 14, 15, 16, 17 are shown on top of the process tunnel. Each chamber 14, 15, l6, 17 has a line 18, 19, 20, 21 connected thereto for supplying or exhausting gases as will be explained. Each chamber l4, 15, 16, 17 has an aperture 23, 24, 25, 26 therein which connects the chamber to the process tunnel 13 for the passage of gas therethrough.

While the holder 12 and wafer 11 are in the hot-zone, process gases are introduced via inlet line 19 through plenum chamber 15 and aperture 24 into the hot-zone 27 of the process tunnel 13 of process tube 10. Process gases in the hot-zone 27 are exhausted through aperture 25 of exhaust chamber 16 and out exhaust line 20. The path of the process gases is indicated by arrows at g the apertures 24, 25.

To maintain the process gases in the center portion of the process tube, gas curtain chambers 14 and 17 are provided having inlet lines 18 and 21 respectively. Gas entering inlet lines 18 and 21 passes through chambers 14 and 17 and apertures 23 and 26' into the end portion of process tunnel 13. The gas passing through the rectangular shaped apertures 23 and 26 is maintained slightly higher than atmospheric pressure and equal or slightly higher than the process gas in the hot-zone 27. Accordingly, no process gas is permitted to leave the ends of the process tunnel and enter the atmosphere. Likewise the gas forming the gas curtain prevents air from entering the process tunnel 13, but may mix with the process gas without affecting the process. The valves and controls for maintaining gas pressures balanced or constant are well known and do not form a v part of this invention. The path of the gas forming the gas curtain is indicated by arrows at apertures 23 and 26.

The roofs or domes 28, 29 of gas curtain chambers l4, 17 are arched and provided with end closures 31. The roof or dome 32 of plenum chamber 15 is arched and provided with end closures 33. The long chamber 15 extends into a heated portion of the furnace which preheats as well as mixes all process gases before they enter the process tunnel 13.

The roof or dome 34 of exhaust chamber 17 is arched and provided with end closures 35. it will be noted that exhaust aperture 25 and exhaust line 20 are made larger than other apertures and lines to insure complete and proper exhaust.

In actual practice, there is a pressure differential along the process tunnel 13 between apertures so that process gases are blocked and restricted to the hotzone 27. This condition continues to exist even though holders 12 with wafers 11 are inserted and withdrawn from the process tunnel or continuously passed through the process tunnel 13 by known means.

Dopant gases have a tendency to condense on the cool end portion of prior art tubes. The present process tube by restricting process gases to the hot-zone portion 27 of the process tunnel 13 substantially eliminates condensation of gases at the cool ends, and wafers are only exposed to process gases under controlled conditions in the hot-zone.

The shape of the components of the process tube are selected to allow ease of manufacture and do not substantially effect the quality of the process. It is believed best to introduce and exhaust gases through chambers having rectangular apertures therein rahter than to connect the intake and exhaust lines 18, 19, 20, 21 directly into the process tunnel 13. Having explained the functions of plenum chamber 15, its advantages are well recognized.

The advantages of a process tube 10 which eliminates dopant deposits, prevents corrosive and toxic gases from entering the atmosphere, permits continuous feeding processes, and provides more uniform processes, should be apparent from the description of the preferred embodiment.

l claim:

1. An improved process tube for a diffusion furnace comprising,

a process tunnel for receiving semiconductor wafer to be processed, said plenum chamber comprising an elongated chamber attached to the top of said process tunnel to provide mixing and preheating of process gases being introduced therein,

an aperture connecting said plenum chamber and said process tunnel,

an inlet in said plenum chamber for introducing process gases, and

a process gas exit point connected to said process tunnel intermediate an end of the process tunnel and said plenum chamber, said exit point providing an outlet for drawing off said introduced process gases before they reach the end of the process tunnel.

2. An improved process tube for a diffusion furnace as set forth in claim 1 wherein said process gas exit point further comprises a chamber having an aperture connecting said process tunnel and an outlet for connecting to an exhaust line.

3. An improved process tube for a diffusion furnace as set forth in claim 1 which further includes a first gas curtain intennediate said plenum chamber and an end of the process tunnel.

4. An improved process tube for a diffusion furnace as set forth in claim 3 which further includes a second gas curtain intermediate said plenum chamber and the opposite end of said process tunnel.

5. An improved process tube for a diffusion furnace as set forth in claim 4 wherein one or more of said gas curtains comprise a chamber having an aperture connecting to said process tunnel and an inlet for connecting an inlet line.

6. An improved process tube for a diffusion furnace as set forth in claim 5 wherein said aperture comprises a slot having a substantially rectangular shape for introducing a curtain of gas which forces process gases to flow through the center of the process tunnel.

7. An improved process tube for a diffusion furnace as set forth in claim 6 wherein the pressure of the gas curtain is higher than the atmospheric pressure and the pressure of the process gas.

8. An improved process tube for a diffusion furnace as set forth in claim 1 wherein said plenum chamber comprises an arch shaped dome attached to the top of a rectangular shaped process tunnel. 

1. An improved process tube for a diffusion furnace comprising, a process tunnel for receiving semiconductor wafer to be processed, said plenum chamber comprising an elongated chamber attached to the top of said process tunnel to provide mixing and preheating of process gases being introduced therein, an aperture connecting said plenum chamber and said process tunnel, an inlet in said plenum chamber for introducing process gases, and a process gas exit point connected to said process tunnel intermediate an end of the process tunnel and said plenum chamber, said exit point providing an outlet for drawing off said introduced process gases before they reach the end of the process tunnel.
 2. An improved process tube for a diffusion furnace as set forth in claim 1 wherein said process gas exit point further comprises a chamber having an aperture connecting said process tunnel and an outlet for connecting to an exhaust line.
 3. An improved process tube for a diffusion furnace as set forth in claim 1 which further includes a first gas curtain intermediate said plenum chamber and an end of the process tunnel.
 4. An improved process tube for a diffusion furnace as set forth in claim 3 which further includes a second gas curtain intermediate said plenum chamber and the opposite end of said process tunnel.
 5. An improved process tube for a diffusion furnace as set forth in claim 4 wherein one or more of said gas curtains comprise a chamber having an aperture connecting to said process tunnel and an inlet for connecting an inlet line.
 6. An improved process tube for a diffusion furnace as set forth in claim 5 wherein said aperture comprises a slot having a substantially rectangular shape for introducing a curtain of gas which forces process gases to flow through the center of the process tunnel.
 7. An improved process tube for a diffusion furnace as set forth in claim 6 wherein the pressure of the gas curtain is higher than the atmospheric pressure and the pressure of the process gas.
 8. An improved process tube for a diffusion furnace as set forth in claim 1 wherein said plenum chamber comprises an arch shaped dome attached to the top of a rectangular shaped process tunnel. 